1. Field of the Invention
The invention relates to a navigation apparatus that detects the position of a movable body. More specifically, the invention relates to a navigation apparatus that accurately corrects the position of a movable body determined using autonomous navigation.
2. Description of the Related Art
In a navigation system, the current position of a host vehicle is accurately estimated, by determining the position of the host vehicle based on radio waves from GPS (Global Positioning System) satellites, and accumulating a travel distance and a travel direction using a vehicle-speed sensor, a gyro sensor, and the like.
However, when the navigation system cannot receive the radio waves from the GPS satellites, the error in position determination performed by autonomous navigation is amplified as the time elapses. As a result, the accuracy of the position gradually decreases.
Accordingly, various methods for correcting the position of the host vehicle determined by autonomous navigation are proposed. For example, in a map matching, the position determined by autonomous navigation is corrected using map data in a navigation system (for example refer to Japanese Patent Application Publication No. 2002-213979 (JP-A-2002-213979)). Japanese Patent Application Publication No. 2002-213979 describes a method in which a road whose position and direction most closely match the position and direction determined by autonomous navigation is selected from map data, and the determined position and direction are corrected by associating the determined position and direction with the selected road.
However, the map data in commercially-available navigation systems is not so accurate. Also, because a road network is represented by straight links that connect intersections (nodes), the road network may not match an actual road configuration. Therefore, the position of the host vehicle may not be sufficiently corrected in the map matching.
Also, a position correction method is proposed, in which the travel path of a vehicle is compared with a road pattern in map data, and the position of the vehicle is associated with a road that is close to the position of the vehicle, based on the degree of matching (for example, refer to Japanese Patent Application Publication No. 8-61968 (JP-A-8-61968)). Japanese Patent Application Publication No. 8-61968 describes a correction method in which it is detected that a host vehicle has passed an intersection or a curve based on a travel path; and map data on the intersection or the curve that matches the travel path is detected by pattern matching. Thus, the position of the host vehicle is corrected.
However, because design is made such that the links intersect each other at 90 degrees at ordinary intersections, when the travel path at an intersection is compared with the road configurations at intersections by pattern matching, the travel path matches almost all the link data relating to intersections. Accordingly, there is a possibility that the travel path matches an intersection that is completely different from the intersection that the vehicle has passed. Also, because the link data is formed by straight lines as described above, it is difficult to detect the link data that matches a curved travel path. Further, because it takes much time to perform the process of pattern matching, it is not appropriate to perform the process of pattern matching in the navigation system.